U.S. Pat. No. 2,497,061 describes alkanedione dioximes as antioxidants for elastomers and drying oils. No mention is made of their use as color improvers for polyolefins during processing either alone or in combination with a phenolic antioxidant. The dioximes of U.S. Pat. No. 2,497,061 are not sterically hindered and fall outside the scope of the instant invention.
The synthesis of sterically hindered oximes is described in Canadian Patent No. 1,053,668. Their use as "spin-labels in molecules of biological interest, as inhibitors of vinyl polymerization, or inhibitors of hydrocarbon oxidation . . . " is suggested within the text. Their use as color improvers during polyolefin processing is not suggested. The bis(sterically hindered oximes) of the present invention are new compounds.
J. L. Brokenshire, et al., J. Amer. Chem. Soc., 94, 7040 (1972); G. D. Mendenhall, et al., J. Amer. Chem. Soc., 95, 2963 (1973); and Canadian Patent No. 1,053,668 all describe the preparation of stable iminoxy radicals from sterically hindered oximes.
European Patent Application 52,573 discloses the use of hydroxylamines plus oximes to improve the color of phenolic antioxidants during preparation of said antioxidants. Diethylhydroxylamine and methyl ethyl ketoxime are preferred components.
U.S. Pat. Nos. 4,566,901 and 4,576,628 disclose oxime ethers which are useful for agricultural purposes as safeners. U.S. Pat. No. 4,028,412 describes .alpha.-hydroxy (benzoin) oximes as chelating agents for copper. The instant sterically hindered oximes are structurally distinguished from the compounds described in these patents.